Abstract
We investigated the effects of forest fragmentation on bird assemblages in an Amazonian savannah landscape with forest fragments that have been isolated for more than 100 years. The study was conducted in areas surrounding the village of Alter do Chão (2°31'S, 55°00'W), Santarém, Brazil. Bird surveys and measurements of tree density were undertaken in 25 areas, with 19 plots in forest fragments of different sizes and six in an area of continuous forest. Data on forest-fragment size, perimeter, and isolation were obtained from a georeferenced satellite image. Variation in number of bird species recorded per plot was not related to vegetation structure (tree density). The number of bird species recorded per plot increased significantly only with fragment area, but was not influenced by fragment shape or degree of isolation, even when considering species from the savannah matrix in the analysis. Fragments had fewer rare species. Multivariate ordination analyses (multiple dimensional scaling, [MDS]) indicated that bird species composition changed along a gradient from small to large forest fragments and continuous-forest areas. In the Amazonian savannah landscapes of Alter do Chão, the organization and composition of bird assemblages in forest fragments are affected by local long-term forest-fragmentation processes. Differences in the number of bird species recorded per plot and assemblage composition between forest fragments and continuous forest were not influenced by forest structure, suggesting that the observed patterns in species composition result from the effects of fragmentation per se rather than from preexisting differences in vegetation structure between sites. Nevertheless, despite their long history of isolation, the forest fragments still preserve a large proportion (on average 80%) of the avifauna found in continuous-forest areas. The fragments at Alter do Chão are surrounded by natural (rather than planted) grassland, with many trees in the savannah matrix and the landscape has vast areas covered by forest, which may have helped to ameliorate the influences of forest fragmentation.
Highlights
Deforestation of tropical rain forests is currently one of the greatest threats to global biodiversity
The results of this study clearly indicate that, in the Amazonian savannah/forest landscapes of Alter do Ch~ao, the organization and composition of bird assemblages are affected by the local long-term processes of forest fragmentation
As found in other studies evaluating the effects of Amazonian forest fragmentation on bird assemblages, forest fragments had fewer rare bird species and the species present in the forest fragments tended to be a subset of those found in sites in the continuous forest
Summary
Deforestation of tropical rain forests is currently one of the greatest threats to global biodiversity. Deforestation results in habitat loss, degradation, and fragmentation of a continuous landscape formerly covered by undisturbed forests. It has been advocated as one of the most negative effects produced by humans, leading many organisms to local extinction and reducing biological diversity. Bird species may respond to fragmentation in ways that are very different from other vertebrates. Previous studies have identified differences in vulnerability to extinction among species or groups of species. Some groups or guilds, such as insectivores, seem to be insensitive; they were the first to disappear after fragmentation, they were the first to return. Most frugivore species disappear from forest fragments after their isolation and few persist in small fragments a 2013 The Authors.
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